1. Field of the Invention
The present invention relates generally to embossed ribs in plates and, more specifically, to a method of designing embossed ribs in plates.
2. Description of the Related Art
Structural topology optimization is a known technology in the aerospace and automotive industry. Only a decade ago, most structural topology optimization had been done with truss-like structures that are used extensively in the aerospace industry. In the automotive industry, structural topology optimization of plates has been used in many components of vehicle design such as floor panels, roof, doors, hoods, etc. Most of these applications in the automotive industry have solved the problem of lightening the structure by locating and shaping holes in plates. Another typical application of structural topology optimization in ground transportation vehicles is in determining the optimum reinforcement of an existing part in order to maximize its performance.
It is known in the automotive industry to stamp body panels for a motor vehicle. The body panels are typically a flat plate with a curvature to fit into the interior of the motor vehicle. To increase the stiffness of the plate without increasing its weight, one possible solution is to stamp the plate and emboss ribs in the plate.
An approach to solve the structural topology optimization of embossed ribs is to use beam elements. A superimposed grid of designable beam elements is added to the undesignable shell element mesh by connecting all nodes within each quadrilateral (or triangular) elements in all possible ways (6 beams/element at most). However, a limitation of this approach is the dependency of the beam mesh on the topology of the shell mesh, which limits the range of orientation for the embossed ribs.
Previous structural topology optimization of plates concerned the issue of finding optimum topology of plate thicknesses. The final result was a locally isotropic plate with two discrete thicknesses optimally distributed in the plate domain (with the possibility of having one or two gages set to zero). However, a limitation of this approach is that the final result is meant to be locally isotropic, missing the orthotropy nature of embossed ribs.
Another approach to solve the structural topology optimization of plates uses a computational procedure where a two-material composite structure is optimally designed by computing the distribution of one of the materials (reinforcing material) within the other (matrix material). The reinforcing material is also locally designed within the matrix in order to determine its tensorial properties point-wise.
Although the above approaches have worked, it is desirable to design an optimally reinforced plate. It is also desirable to design embossed ribs that are optimally located and orientated in plates. It is further desirable to provide a process that will be more accurate in the representation of the structural properties of embossed plates than the former two-gage thickness distribution of isotropic plates. Therefore, there is a need in the art to provide a method of designing embossed ribs in plates.
Accordingly, the present invention is a method of designing embossed ribs in plates. The method includes the steps of inputting data of a loaded un-embossed plate and computing orthotropic properties of an embossed ribbed plate material for the plate. The method also includes the steps of running structural analysis and obtaining stress on the plate. The method includes the steps of computing stiffness of the plate. The method includes the steps of computing the optimum orientation of the embossed ribs at each point in the plate using the computed stresses and orthotropic properties of the plate. The method includes the step of computing the gradient of objective function and constraints. The method includes the steps of solving local optimization problem to obtain a new location and spacing of the embossed ribs in the plate and outputting orientation, location and spacing of the embossed ribs in the plate.
One advantage of the present invention is that a method of designing embossed ribs in plates is provided for motor vehicle panels. Another advantage of the present invention is that the method uses special stiffness properties for membrane and bending deformations separately. Yet another advantage of the present invention is that the method combines stiffness properties of flat plates and embossed ribbed plates to solve the structural topology optimization of embossed ribs. Still another advantage of the present invention is that the method provides an optimally reinforced plate, the one with embossed ribs optimally located and oriented, which is locally orthotropic, that is, with two principal (in-plane) directions, one parallel to the ribs and another orthogonal to them. A further advantage of the present invention is that the method can be used to increase the stiffness of plates without increasing weight, allowing a reduced plate thickness, and therefore, a lighter plate. Yet a further advantage of the present invention is that the method is more accurate in the representation of the structural properties of embossed plates than the former two-gage thickness distribution of isotropic plates.
Other features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.